Imatinib was developed to target specifically the deregulated tyrosine kinase activity of the oncoprotein BCR-ABL in chronic myeloid leukemia (CML) and it has high specificity against its major kinase target. In a surprising and unexpected finding in 2007, NQO2 was identified as the first non-kinase target of imatinib in two independent studies. Imatinib was found to bind potently and specifically to NQO2 resulting in inhibition of catalytic activity of the enzyme. One of the conclusions of these two studies was that inhibition of NQO2 may contribute to the therapeutic activity of imatinib in CML cells. In this proposal, we will define the outcome of specifically targeting NQO2 in CML. Levels of NQO2 have not been examined in human CML and in aim 1 we will characterize NQO2 levels in a panel of imatinib-naive and imatinib resistant archived CML patient samples. In aim 2, we will examine whether specific targeting of NQO2 using novel mechanism-based (suicide) inhibitors developed in our laboratory results in antiproliferative activity in human CML cell lines. We will also validate the role of NQO2 in the proliferative activity of CML cells by employing anti-NQO2 shRNA and characterize the effect of stable knockdown of NQO2 on CML growth. BCR-ABL stability is known to be influenced by interactions with other proteins. In aim 3, we will therefore examine whether there is a protein-protein interaction between NQO2 and BCR-ABL, whether this interaction is inhibited by imatinib, whether it leads to increased stability of BCR-ABL and whether it depends on the catalytic activity of NQO2. The proposed studies will characterize the potential role of NQO2 in the therapeutic activity of imatinib and define the outcome of specifically targeting NQO2 as a therapeutic approach in CML. PUBLIC HEALTH RELEVANCE: Imatinib has been found to bind potently and specifically to NQO2 resulting in inhibition of catalytic activity of the enzyme. The implication of this work is that inhibition of NQO2 may contribute to the therapeutic activity of imatinib in chronic myeloid leukemia (CML). The proposed studies will define the outcome of specifically targeting NQO2 in CML. The development of novel small molecule suicide inhibitors of NQO2 may provide a novel therapeutic approach in CML.